Carborane Substituents Promote Direct Electrophilic Insertion over Reduction-Metalation Reactions

• Published in: Angewandte Chemie International Edition Vol. 55; no. 14; pp. 4596 - 4599
• Main Authors: Man, Wing Y., Ellis, David, Rosair, Georgina M., Welch, Alan J.
• Format: Journal Article
• Language: English
• Published: Germany Blackwell Publishing Ltd 24-03-2016; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: bis(carboranes); fluxionality; metalation; metallacarboranes; two-electron reduction; fluxionality; metallacarboranes; metalation; bis(carboranes); two-electron reduction
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201600635

Two‐electron reduction of 1,1′‐bis(o‐carborane) followed by reaction with [Ru(η‐mes)Cl2]2 affords [8‐(1′‐1′,2′‐closo‐C2B10H11)‐4‐(η‐mes)‐4,1,8‐closo‐RuC2B10H11]. Subsequent two‐electron reduction of this species and treatment with [Ru(η‐arene)Cl2]2 results in the 14‐vertex/12‐vertex species [1‐(η‐mes)‐9‐(1′‐1′,2′‐closo‐C2B10H11)‐13‐(η‐arene)‐1,13,2,9‐closo‐Ru2C2B10H11] by direct electrophilic insertion, promoted by the carborane substituent in the 13‐vertex/12‐vertex precursor. When arene=mesitylene (mes), the diruthenium species is fluxional in solution at room temperature in a process that makes the metal–ligand fragments equivalent. A unique mechanism for this fluxionality is proposed and is shown to be fully consistent with the observed fluxionality or nonfluxionality of a series of previously reported 14‐vertex dicobaltacarboranes.
Take two: Two‐electron reduction of 1,1′‐bis(o‐carborane) and subsequent metalation with {Ru(mes)}2+ results in a 4,1,8‐RuC2B10 species. A further two‐electron reduction allows a direct electrophilic insertion reaction promoted by the carborane substituent for the addition of a second metal fragment and the formation of 1,13,2,9‐Ru2C2B10. A mechanism is proposed to rationalize the observed fluxionality of the products.